1. Field of the Invention
This invention relates to assembly machines and more particularly to an assembly machine, adapted to assemble articles formed from several parts, having a positive positioning mechanism.
2. Description of the Prior Art
Assembly machines of the variety disclosed herein are particularly suitable for assembly of an article made from a plurality of relatively small parts. Assembly machines operate at a relatively high speed. During assembly of an article a portion of the article is fed onto a movable assembly table. The article is positioned at a station on the assembly table. The assembly table is then indexed, so that the article is moved to a work station where any of a number of operations can occur such as: adding additional components, drilling, taping, screwing, pressing, rivoting, reorienting, testing, removing, or any other desired operation. After a slight time delay the assembly table is again indexed so that the article moves to successive work positions where all the required operations are performed. At any time numerous articles in various states of assembly will be located on the assembly table. The article can be fed onto and removed from the assembly table by any of a variety of means well known in the prior art. It can readily be appreciated, that, since all operations on the article to be assembled must be coordinated with the location of the work stations during the dwell portion of the machine cycle, it is highly desirable that the work stations location be determined with a high degree of accuracy. That is, the various tooling is set to perform a predetermined operation on the article when it is at a given work position. If the article is not at the correct position, machine jams or damage to the article can occur. Exact high speed positioning becomes especially critical as the assembly speed is increased.
The assembly machine can have a rotatable assembly table with the stations spaced around the outer perimeter of the table. Various assembling and finishing operations can be performed on the article positioned in the station as the rotatable assembly table is indexed, in steps, around the machine. The articles can be loaded onto the assembly table by means of the well known vibratory bowl feeders, manually, or by other suitable means.
Assembly machines having an annular assembly table which can be rotated around a main center support column are well known in the art. U.S. Pat. No. 3,065,530 to Merchant et al. and U.S. Pat. No. 3,231,968 to Swanson exemplify prior art assembly machines having a rotatable assembly table. An indexing unit moves the assembly table of the machine at intervals or steps around the center support column. The stations, containing the article, are stopped at the work positions during indexing steps. During these dwell portions of the machine cycle, the required operations are performed on the article. A problem frequently encountered with the prior art units is that if the indexer is adequately protected from jam conditions with a torque limiting device between the indexer and the indexing table, the position accuracy of the indexer is dependant upon the reliability of the torque limiting device to return to an exact position. It is desirable to have a positioning system which positively and accurately positions the assembly table with a high degree of accuracy during the dwell portion of each machine cycle.
Due to the above problems prior art assembly machines which require long service accuracy are not provided with an overload mechanism between the indexer and assembly table.